UV rays and horses' eyes

What are UV rays? They are rays emitted by the sun. There are several types, and they vary in danger depending on how well they are filtered by the atmosphere. Rays that are not filtered by the atmosphere (UVA and UVB) can pose risks to the skin (horses with white marks, sunburn), but also to the eyes! The danger of UV rays depends on geographical location, altitude, and time of day (most dangerous between 10 a.m. and 2 p.m.).

UV rays: what are the risks for my horse's eyes?

Fortunately, most UV rays are filtered out. UVC rays are filtered by the atmosphere, and UVA and UVB rays are filtered by the eye, thanks to several anatomical structures.

The horse's cornea

It is a very thin layer of cells. It is the only transparent tissue in the body and enables vision. Located at the front of the eye, the horse's cornea absorbs some of the UV rays it receives, thereby protecting the lens and retina. Even though its upper layer is constantly renewing itself, these cells are sensitive to cumulative effects. Excessive exposure of the cornea to UV rays can cause inflammation, resulting in a burning sensation: this is known as keratitis.

The lens

It is located behind the cornea and iris. Its role is to focus light onto the retina. It is particularly sensitive and also absorbs a large proportion of UV rays. However, the more the eyes are exposed without protection, the more the lens ages. It loses its transparency, becomes cloudy, and ultimately increases the risk of developing cataracts. Its filtering function is essential. Horses that have undergone cataract surgery, where the lens has been removed or replaced with an implant, must be protected from UV radiation in order to protect the retina.

The horse's retina

It covers the back of the eye.The horse's retina is responsible for transmitting light signals to the brain. Sunlight is thought to accelerate the aging of the retina.

The eyelids

They provide mechanical and physiological protection for the eye through the blinking reflex and by spreading tears across the cornea. They are highly exposed to external elements, particularly UV rays. Horses' eyelids are susceptible to cancer. According to the Skin Cancer Foundation, 10% of all skin cancers in humans are located on the eyelid. Exposure to UV rays, especially UVB rays, is the main cause of eyelid tumors. Exposure to UV rays is cumulative. This means that you cannot repair damage that your skin or eyes have suffered in the past. However, you can reduce the risk of making things worse. So start taking additional protective measures against the sun now, especially for horses with a history of eye disease (cataracts, uveitis, keratitis, ulcers, etc.).

How can I protect my horse from UV rays?

There are many products available today to protect horses' eyes from insects. However, few of them filter UV rays. Equine eye protection often darkens the eyes. This is good for limiting glare, but it is extremely harmful if UV rays are not filtered. This is because the pupil dilates more in the shade, allowing even more UV rays to pass through if they are not filtered. Read the instructions carefully before purchasing a mask or hard goggles for work. For hard goggles for working horses, the color of the lenses has virtually no effect on the level of UV protection. Whether the lenses are transparent, gray, or brown, with or without a mirror effect, this matters much less than the UV protection built into the lenses. However, pay attention to the shape and size of the frame of the hard goggles; the closer they are to the head, the more effective they will be against UV rays.

Article written by Estelle Guilbaud—Optician and optometrist specializing in equine vision